Figure 4.

AQP4 regulates interstitial fluid resorption and solute clearance. A, top panel: baseline brain water content of glial-conditional Aqp4 knockout (cAqp4^−/−) mice and litter controls (f/f) at various stages of postnatal development suggests a role for AQP4 in resorption of brain water. At postnatal days P15, P28, and P70, the brain water content was significantly higher in cAqp4^−/− mice than in litter controls. Bottom panel: brain water content is increased also in adult cAqp4^−/− mice. [From Haj-Yasein et al. (55), with permission.] B: Aqp4 deletion increases extracellular space (ECS) volume without affecting tortuosity, as measured by real-time iontophoresis with tetramethylammonium. [From Yao et al. (204), with permission.] C: clearance of intraparenchymally injected mannitol is reduced in mice lacking AQP4. D: hypothetical pathway for brain water flow and solute clearance, based on two-photon imaging of intracisternally injected fluorescent tracers and accumulation of intraparenchymally injected radiotracer (see text for explanation). [C and D from Iliff et al. (69). Reprinted with permission from AAAS.]